The present invention relates to an apparatus for analizing liquid samples, and more particularly to a liquid sample analizing apparatus suitable for use in measuring optical characteristics of a liquid sample which is prepared by mixing a material to be examined with a reactive reagent in a reaction tube and then introduced into a flow cell.
Recently, the rate assay method (hereinafter referred to as the rate method) has been extensively employed in the field of clinical biochemical analysis. The rate method is fundamentally small in endogenous error, and therefore superior in accuracy of measured value to the colorimetric measurement. On the other hand, the rate method has a drawback that the measured value is readily affected by the temperature of sample solution under measurement. For the above reason, in a practical analizing apparatus, it is required to rapidly heat or cool a sample solution to a constant temperature, and to maintain it at the constant temperature during the rate measurement. The rate method may be carried out with such an analizing apparatus as disclosed in U.S. Pat. No. 3,728,080. In such an analyzing apparatus, a sample solution is introduced from a reaction tube into a flow cell to permit observation of absorbance change depending on the sample solution. According to the rate method, the sample solution is held in the flow cell for a predetermined period of time so that the absorbance of the sample solution is measured a plurality of times to obtain changes in absorbance at the predetermined period of time, resulting in a lower speed for sample processing in the rate method than in the colorimetric measurement.
In conventional analizing apparatus for rate assay, a sample solution is introduced from a reaction tube into a single flow cell, and after the photometric operation for rate assay has been completed, a different sample solution is introduced from a next reaction tube into the same flow cell to conduct a next rate assay. In such an analising apparatus using a single flow cell, when transferred from the reaction tube to the flow cell, the sample solution is cooled by the air to a temperature which is lower than a temperature required in measuring the absorbance. Therefore, prior to the photometric operation, thus an operator has to wait for a while until the temperature of the sample solution in the flow cell is increased to reach a predetermined value. That is, the time taken to measure one sample solution with the conventional apparatus is equal to the sum of the time for temperature stabilization and the time for rate measurement (or photometric operation), so that this sum determines the sample processing speed in the conventional apparatus.
A plurality of flow cells are employed in the present invention. The use of two flow cells is not novel and one of the two flow cells is used for a sample solution while the other for a reference solution to compare two photometric signals resulting from the sample and reference solutions so as to define a measured value based upon the comparison in such a conventional photometer utilizing two flow cells. As will be clarified later, the function of a plurality of flow cells employed in the present invention is entirely different from the function of those used in the conventional photometer.